But then, a widely publicized but since-retracted study in the Lancet journal linked vaccines with autism, and autism activists like Playboy model Jenny McCarthy spread scary stories of watching their children regress after being vaccinated — you’ve heard the tales, unless you’ve been hiding in a hole.

Multiple studies have disavowed any link between immunization and autism, but the power of storytelling is hard to counter with data, as evidenced by the increasingly vocal numbers of parents who refuse to vaccinate their children and a growing percentage who agree to vaccinate but do so according to their own schedule, spreading out the required immunizations over a much longer time period than is recommended by public-health organizations.

It’s this latter group that a team of researchers in Oregon — a state that has historically had a high number of parents opting out of vaccinations for religious reasons — decided to study. The researchers found that “shot limiting” — when parents restrict the number of shots their child receives at each doctor’s visit — increased from 2.5% children in 2006 to 9.5% in ’09. The altered schedules ultimately resulted not only in increased intervals between vaccinations but overall lower levels of immunization, according to the research published Monday in Pediatrics.

“We’ve been concerned about vaccine hesitancy for a while in Oregon,” says Steve Robison, an epidemiologist in the Oregon Health Division and the study’s lead author. “It’s published in books, it’s on the Internet, and in Portland, you may even hear it from your barista.”

Researchers from the Oregon Immunization Program took a look at the various alternative schedules out there, everything from published advice to homegrown plans, and decided to focus on two specific alternative schedules that parents commonly follow. Both are created by physicians — Dr. Stephanie Cave and Dr. Robert Sears — and both limit the number of shots received at any particular visit to one or two, but Cave’s plan is more restrictive.

Other studies have surveyed parents about their practices, but this was the first study to analyze immunization records. Researchers pored over records of babies born in the Portland area between 2003 and ’09 and tracked them up to 9 months of age, a period that covers the 2-, 4- and 6-month well-child visits at which infants are supposed to receive three or four injections at a time. They found that 4,502 of 97,711 children, or 4.6%, met the definition of consistent shot limiters. By 9 months of age, these babies had received fewer injections — 6.4 compared with 10.4 — but had logged more doctor visits at which they received immunizations — 4.2 vs. 3.3 — than children who followed the recommended schedule. Most delayers never ended up receiving all the recommended vaccines. In Oregon, 16% of 2-year-olds are not up-to-date with the standard schedule.

“They’re getting less protection for more hassle,” says Paul Cieslak, medical director for the Oregon Immunization Program. “The main problem with alternative schedules is they’re tough to stick to.” The current vaccination schedule calls for five visits between birth and 15 months for the primary childhood vaccines (some preschool booster shots and a final dose of hepatitis A come later), but some alternative schedules spread the shots out over nine visits within that same span. “It is harder for parents to pull it off,” says Cieslak.

Parents who choose to delay often do so because they’re concerned about sticking their baby with needles multiple times or worried that too many shots clustered in one visit can trigger complications. But vaccine advocates note that no evidence has been found to show that delaying vaccination is helpful for babies — and it can be harmful. “There is absolutely no scientific data that shows a delayed schedule is any safer,” says Wendy Sue Swanson, a pediatrician who blogs for Seattle Children’s Hospital under the handle Seattle Mama Doc. It carries exactly the same amount of risk. You can still have life-threatening side effects, but you increase the time your child is not protected.”

Up to 40% of children in Oregon experience some degree of delay in their vaccination schedule, perhaps due to a shortage or a conflict with a doctor’s appointment; that figure is on par with national figures. About 1 in 5 has parents who have chosen to delay the child’s immunizations on at least one visit.

“With the best of intentions, parents are wanting to do this, and doctors are accommodating parents who are nervous about kids getting lots of shots at one visit,” says Cieslak. A study in Washington state, which has the country’s highest proportion of unvaccinated kindergartners, found that 60% of pediatricians are comfortable with alternative vaccine schedules. “The problem is that with some diseases, you need to get vaccinated early. Whooping cough is much more serious in infancy. Pneumococcal disease and haemophilus are much more serious under the age of 3.”

Ultimately, vaccination as a linchpin of childhood health is a victim of its own success: immunization has been so skillful at eradicating deadly disease in the U.S. that few parents have any firsthand knowledge of someone who’s contracted a vaccine-preventable condition. That has made plunging a needle into a newborn a tough sell.